1. A study on Loviisa NPP (VVER-440) dose rate measurement's ability to detect small primary-to-secondary coolant leaks A. Ketolainen
ISOE European Symposium on
Occupational exposure management at nuclear facilities
Turku, Finland, June 2008
Fortum
Antti Ketolainen

2. Table of contents Introduction SEKUN computer code
Dose rate measurements
Results
Conclusions
Fortum
Antti Ketolainen

3. Introduction
At Loviisa NPP coolant leaks will be detected on the basis of different parameters
Low liquid level of pressurizer or high liquid level of steam generator can indicate primary-to-secondary coolant leaks
Different kinds of coolant leak incidents and accidents has specified operating procedures which will be executed when certain operating limits will be exceeded
Primary-to-secondary coolant leak will raise activity at the secondary circuit
Small primary-to-secondary coolant leaks can be distinguished from the other coolant accident -transients by the information of the dose rate measurements
Fortum
Antti Ketolainen

4. SEKUN computer code
1989 documented FORTRAN code (H. Wallin's licentiate thesis: "Computer-based calculation model for radiation doses caused by reactor accidents")
developed to calculate radiation doses and activity releases to the power plant's environment at primary-to-secondary coolant leak transients
Primary circuit: 1 calculation node
Secondary circuit: 5 calculation nodes
2 steam generators, 4 nodes (steam and liquid sides)
damaged steam generator with supposed coolant leak
one steam generator for all other steam generators
1 node for feed water in the tank and condenser
Fortum
Antti Ketolainen

5. SEKUN node model
Fortum
Antti Ketolainen

6. SEKUN Input data = f(time) Thermohydraulic rates (APROS)
Nuclide specific activity concentrations of the primary and secondary coolants
Dose rate measurements were programmed to the code during the project
The SEKUN calculates activity concentrations for every node
Monitored dose rates in the primary and the secondary circuits are estimated on the bases of the calculated activities
Fortum
Antti Ketolainen

7. Dose rate measurements
Secondary coolant's radiation dose measurement in blowdown systems of steam generators (RY)
1,25"x1" NaI-scintillator,energy window: 0,15 - 2,2 MeV
Radiation dose measurement of the secondary circuits steam side (RA):
RA-911
NaI-scintillation detectors, 0,2 - 2,2 MeV (noble gas)
Also dose rate measurement for higher gamma energies (RAxxR921) (not included in this presentation)
Fortum
Antti Ketolainen

8. Dose rate measurements
Interpretation of the secondary coolant's measuring results requires information about specific activities in the primary circuit
Primary coolant's radiation dose measurement (TV04)
1"x0,5" NaI-scintillator, 0,15 - 2,2 MeV
measuring range: *1010 kBq/m3
Fortum
Antti Ketolainen

9. The basic idea of the study
Thermohydraulic simulations: APROS 5.04
Activity calculations: SEKUN
2 kg/h is the maximum allowed leak (power plant's specifications) before the actual leak was used as a starting hypothesis
Fortum
Antti Ketolainen

10. Calculation
Different operational conditions and primary-to-secondary coolant leaks were modelled with APROS 5.04 simulation software
Fortum
Antti Ketolainen

11. Results 0,5 kg/s leakage in power operation
Primary (TV04) and secondary (RY) coolant's radiation dose measurements
Fortum
Antti Ketolainen

12. Results 0,5 kg/s leakage in power operation
Radiation dose measurements at the secondary circuit steam side (RA-911)
Fortum
Antti Ketolainen

13. Results 0,5 kg/s leakage in hot standby
Primary (TV04) and secondary (RY) coolant's radiation dose measurements
Fortum
Antti Ketolainen

14. Results 0,5 kg/s leakage in hot standby
Radiation dose measurements at the secondary circuit steam side (RA-911)
Fortum
Antti Ketolainen

15. Conclusions
Secondary coolant's radiation dose measurement (RY) in power operation
Fortum
Antti Ketolainen

16. Conclusions
Secondary coolant's radiation dose measurement (RY) in hot standby
Fortum
Antti Ketolainen

17. Conclusions
Radiation dose measurements at the secondary circuit steam side (RA-911) in power operation
Fortum
Antti Ketolainen

18. Conclusions
Radiation dose measurements at the secondary circuit steam side (RA-911) in hot standby
Fortum
Antti Ketolainen

19. Conclusions
> 0,5 kg/s primary-to-secondary coolant leaks can be identified with dose rate measurements
Information of the primary circuit's activity is also required for identification of primary-to-secondary leak
Activity concentrations which have been identification limits for primary-to-secondary coolant leaks were correct
Better protection from the background radiation for RA meters would make easier the identification of leak
Fortum
Antti Ketolainen

20. Thank You!!! Antti Ketolainen Design engineer FNS Ltd.
Fortum
Antti Ketolainen